Method of production of reclaimed rubber in discrete particle form



July 23, 1957 E, F. SVERDRUP METHOD OF PRODUCTION OF RECLAIMED RUBBER 1N Insomma PARTICLE FORM Filed Feb; l2, 1953 INVENTQR EDWARD F WERD/Hl? ATTORN EYS :fuit

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METHOD OF PRODUCTIN F RECLAIMED RUBBER IN- DSCRE'FE PAR'HCLE FURM Edward F. Sverdrup, Buffalo, N. Y., assigner to U. S. Rubber Reclaiming Co. Inc., Buiialo, N. Y.

Application February 12, 1953, Serial No. 336,514 Claims'. (Cl. 26o- 2.3)

This invention relates tothe reclaiming; ofv rubber and like materials, and more particularly to the production of reclaimed rubber in discrete-particle form.

In the various methods ofv reclaiming rubber as heretofore practiced, the reclaim is produced in dense or agglomerate form. Even in the processes wherein the scrap rubber isbrokeri up` into' crumb and treated at high ternperatureA in crumb form, it is treated as an agglomerate massirr which heat' has to be transferred through one o1' many parts of the mass in order to reach the interior portions or particles. As a consequence, some particles are over-heated while others do not receive enough heat for satisfactory plasticati'on, and, even. if. the rubber remains in crumb form throughout. the heat treatment, reclaiming cannot be considered' complete until. it has been put through a refining treatment to get rid of the still unplasticated particles of un-treated or under-treated rubber; They product is accordingly in the form of'de'nse` or crepealikemasses.

For manyr purposesfi-t is most advantageous to supply reclaimed rubber in small" pieces which `may be referred to as being in discrete particle, granu1ar, pelletized or crumb form. For greater clarity, we shall reserve the term: pelleti-zedi reclaim, for' reclaimed. rubber which is broken up'ror.- reformed into small piecesafter having been. compacted in massive form. We shall describe all such products generally as discrete particle form; withf out implying that the particles-are crumb which has remained as such during reclaiming.

I have`found,A moreover, that rubber'can be reclaimed witlrmany'A advantages by keeping it in crumb form while` subjecting it to reclaiming temperature, with or without mechanical working, in a iluent hea'texchange and parting medium, suci asl aipowder which will coat the surfaces of the rrubber particles and lubricate them. against adhesion to other rubber particles. Such a medium servesbotli to lubricate the rubber particles, preventing their re-adherence'when the rubber scrap becomes plastic during the devulcanizing operation, and to transfer heat to and from heat control surfaces such as the walls of jacketed chambers, or heated impellers.

Iii rubber-reclaiming` operations according to.V this process,f surprising improvements in effectiveness may be obtained by preheating the powder. so. that it carries. all or substantially all the heat necessary to bring the rubber withwhichit is mixedup to devulcanizing temperature. The d'ifliizultly-controlled devulca-ni'zingy operation. is ini` tiatedl much faster andv mucl'rmore` uniformly by intermingling the comminutedA` rubber intimately with such aheated powder,- which comes into immediate. contact with., substantially all the. particles ofk pre-comminuted rubberl andi immediately initiates the, devulcanizing operation uniformly throughout the mass.

Bearing; in mind that the. devulcanizing operation in.- voiriesA thesbreakingt down; of: large molecules; into smaller. ones;by scission; induced by thermal, mechanical, and/ or chemical means Giust" as vulcanization is: theresult' of accordance with the invention.

uniting pluralities of molecules into larger ones by crosslinking through sulfur) it will be understood that, when l A wide range of liuent media having good heat-trans'-v fer and parting' properties may be employed. Powders 99% of which pass a 325-1nesh screen give effective' r'esults. Examples of powders adapted for effective s'e in accordance with the invention are Whiting, activated' carbon, talc, barytes, mineralite mica, graphite, lithopone, aluminum silicate, cryolite, calcium silicate, and other suitable materials which will stand the temperatures used. While the minimum usefulV proportion depends upon the character of the powder and' the rubber, it may be said in general that a proportion of powder less than 10% ofthe 20-mesh crumb will not effectively surround and heat theV rubber particles, and quantities above 3000% of the' crumb areV ineliicient. The minimum quantity of any particular dusting powder which gives eiective results depends to a lar'ge extent on the heat capacity of the powder and upon temperature conditions desired'. Such minimum amount' can beV computed from the following data:

Desired` devulcanization temperature= Dusting powder temperature: p

Initial crumb temperature=c Speciiic heat of rubber=h Specific heat` of. dusting powder=H Amount of dusting material-:XA Amount of rubber=l (unity) According tol the following' equation: HX(p-r)=1h(rc) A wide variety of types of rubber may be treated in Among them may be mentioned natural rubber, (StR-SV (Enna-S), neoprene, butyl rubber, and copolymers4 of' butadiene and' acrylonitrile (Buna-N').

Treating times may run from a minute and ahalf to an hour or' more, but effective results can ordinarily be obtained in three minutes or less by a procedure s'uch as exemplified in the drawing;

In carrying out the procedure in the exempliiied manner, a suitable powder such as Whiting is conducted from a storage bin itl and/ or return conveyor'i' to a surge' hopper 12'and thence through a feeding' means ld which feeds powder at ay constant rate to a rotary kiln le which' is indirectly heated under controi of a thermostat 17. From the.- kiln it is delivered at a temperature of from 450 F. to 750 F. to an insulated rapid mixer 18, in whichtemp'erature may be maintained by heating elements i9.V

Crumbk rubber! which will pass a 30u-nosh and be r'etained on a 40mesh screen is carried through a continuous mixer 20 to which reclaiming olis and/or suitable chemical or. other reclaiming agents are introduced by a'fpro-V portioning pump 22. The material from the crumb mixer 2t) is:fed by a conveyor 23 into the insulated mixer i3 t'o'- gether with hot powder from kiln lo. This powder,` as it is intensively mixed with the crumb rubber by the iSl acts as heat transfer medium and as a dustingpowder tokeepvthe rubber particles separate and in free motion. Thus the individual particles of the crumb rubber are' heated rapidly and uniformly to effective devulcanizingf' temperature.

The mass of powder'mayv also serve to control oxidation of each particleby-y eectively' surrounding' if with Patented July 23,y 1957` inert powder particles so as to prevent undesirable access of oxygen thereto. In the chamber 18, the loose mixture of hot Whiting and crumb rubber throughout rapidly reaches a uniform temperature in the desired range, e. g., from 300 to F. to 450 F. Y Y

Due to the very rapid heating of the rubber made possible by this method the devulcanization reaction begins at once, and proceeds'uniformly throughout all of the rubber. The treatment may continue for a long time as in the old pan process, in which case heating may be continued by heat applied through the mixer wall which, by virtue of the constant agitation of the mass of powder, will be uniformly distributed through the rubber; or the treatment may be for a very short period, according to the Elgin and Sverdrup Patent No. 2,415,449, dated February l1, 1947, in Which case the heat initially supplied in the powder and conserved by efficient insulation on the mixer 1'8 will ordinarily suffice Without application of vadditional heat at 18.

As the mixture of powder and rubber crumb leaves the mixer 18, it falls into a cooler Z5 which rapidly cools the mass to a temperature of from 70 F. to 150 F. From the cooler, the mass is fed by conveyor 26 onto a vibrating screen 27 which may be an 80-mesh screen vibrated by a vibrating means 28 and through which the excess Whiting falls onto a conveyor 11, whence it is conducted back to surge hopper 12.

There may be produced devulcanized crumb of a size such that 98% thereof will pass a 20-mesh screen.

While there are given below certain specic examples of this invention and its application in practical use and also certain modifications and alternatives, it should be understood that these are not intended to be exhaustive or to be limiting of the invention. On the contrary, these illustrations and the explanations herein are given in order to acquaint others skilled in the art with this invention and the principles thereof and a suitable manner of its application in practical use, so that others skilled in the art may be enabled to modify the invention. and to adapt it and apply it in numerous forms, each as may be best suited to the requirement of a particular use.

Example 1 l650 parts of Whiting all of which would pass a 100 mesh screen and 98% of which Would pass a 200 mesh screen is heated to 588 F. in an indirectly heated rotary kiln. The hot Whiting is then rapidly mixed with 150 parts by weight of a rubber-oil mix containing 100 parts of 30-40 mesh vulcanized rubber crumb (made from tire scrap containing about equal parts of natural rubber and GR-S) mixed with 0.3 part xylyl disuliides, l2 parts of a petroleum oil, such for example, as one having a viscosity at 100 F. of 150-160 seconds, an A. S. T. M. flash point of 325-330 F., a iire point of 370-380 F., a pour point test of 30 F. max., a color NPA of 2, a Conrad carbon of .02%, a specific gravity of 0.9309, and an A. P. I. gravity of 20.5; 4 parts of a resinous physical agent, such for example as one having a specific gravity of about 1.06, a softening point (ring and ball 135) of about 145 F., and a acid number of 146; and 3 parts of a mixture of terpene hydrocarbons having a specific gravity of 0.872 at 15.2 C., an index of refraction at 20 C. of 1.482, Engler distillation data giving:

and a flash point, open cup of 136 F., and which parts to it an initial temperature of 400 F.

7 5 inhibit cohesion thereof and reclaims the rubber particles,

This mixture is held for 3 minutes in a thermally insulated mixer and then discharged into a cooler prior to being passed over a 60 mesh sieve to remove the excess Whiting. The rubber portion when passed through a tight laboratory mill forms a sheet with a degree of plasticity and softness which shows effective devulcanization.

Example 2 vulcanized crumb which has remained in discrete particle form most of the particles whereof will pass a 20-mesh screen.

Example 3 1100 parts of the same Whiting as that of Example 2 is heated to 550 F.,'as at 16, and mixed as at 18 for about three minutes with the rubber-oil mix of Example 2. A devulcanized crumb, most of which will pass a 20- mesh screen, is Produced.

Example 4 A procedure similar to that of Example 3 except that 180 parts of Whiting are employed, with the mix remaining in chamber 18 for `20 minutes; yielding a devulcanized crumb as above.

Example 5 161.5 parts of Whiting as in Example 1 is heated to 450 F., and mixed with 100 parts of a rubber-oil mix as set forth in Example 1 except that 20-mesh crumb is used, for 5 minutes; yielding a devulcanized crumb as above. y Y f Example 6 3,000 parts of Whiting is heated to 427 F. and mixed with parts of a rubber-oil mix, as set forth in Example 5, for 5 minutes; yielding a devulcanized crumb as above.

- Example 7 240 parts of barytes similarly powdered is heated to 750 F. and mixed with 100 parts of a rubber-oil mix, -as set forth in Example 5, for 4 minutes; yielding a devulcanized crumb as above.

Example 8 400 parts of graphite similarly powdered is heated to 480 F. and mixed With 100 parts of a rubber-oil mix, as set forth in Example 5, for 5 minutes; yielding a devulcanized crumb as above.

Example 9 360 parts of carbon black of a similar or lesser neness is heated to 500 F. With 100 parts of a rubber-oil mix, as set forth in Example 5, for 10 minutes; yielding a devulcanized crumb as above;

I claim:

l. The method of reclaiming vulcanized rubber scra which comprises preheating a particle separating powder to a temperature of between about 450 F. and 750 F., immediately mixing the powder with comminuted vulcanized rubber scrap and subjecting a loose mass of the mixture in the absence of compacting pressure to a mechanical agitation for a sufficient time that the heat of the powder softens the surfaces of the rubber particlesy sufiiciently to cause the'powder to adhere thereto and form a protective coating about the tends to inhibit oxidation of the rubber particles and to rubber particles whichand discharging the powder-coated reclaimed rubber particles as discrete particles, the powder being present in a volume of at least 23% of the volume of the scrap.

2. A method as set forth in claim 1 wherein the materials are continuously mixed and the mixture then passed through a temperature-maintaining zone.

3. A method as set forth in claim 2 wherein said zone is enclosed.

4. A method as set forth in claim 1 wherein excess powder is removed from the comminuted particles after the treatment.

5. A method as set forth n claim 1 wherein 100 percent of the powder will pass a 100-mesh screen and only 2 percent will remain on a 20G-mesh screen.

6. A method yas set forth in claim 1 wherein the powder is Whiting.

7. A method as set forth in claim 1 wherein the powder is carbon black.

8. A method as set forth in claim l wherein the powder is talc.

wherein the powder wherein the powder References Cited in the file of this patent UNITED STATES PATENTS 693,151 Price Feb. 11, 1902 1,024,937 Heller Apr. 30, 1912 1,133,952 Gare Mar. 30, 1915 1,963,943 Gross June 19, 1934 2,278,826 Castello Apr. 7, 1942 2,408,296 Cotton etal Sept. 24, 1946 2,415,449 Sverdrup Feb. 11, 1947 2,461,193 Banbury et al Feb. 8, 1949 2,600,430 Riblett June 17, 1952 2,640,035 Brown et a1 May 26, 1953 2,767,149 Wendrow Oct. 16, 1956 FOREIGN PATENTS 580,051 Great Britain Aug. 26, 1946 

1. THE METHOD RECLAIMING VULCANIZED RUBBER SCRAP WHICH COMPRISES PREHEATING A PARTICLE SEPARATING POWDER TO A TEMPERATURE OF BETWEEN ABOUT 450*CF. AND 750*F., IMMEDIATELY MIXING THE POWDER WITH COMMINUTED VULCANIZED RUBBER SCRAP AND SUBJECT A LOOSE MASS TO THE MIXTURE IN THE ABSENCE OF COMPACTING PRESSURE TO A MACHANICAL AGAITATIXXX XX A SUFFICIENT TIME THAT THE HEAT OF THE POWDER SOFTENS THE SURFACE OF THE RUBBER PARTICLES SUFFICIENTLY TO CAUSE THE POWDER TO ADHERE THERETO AND FORM A PROTECTIVE COATING ABOUT THE RUBBER PARTICLES WHICH TENDS TO INHIBIT OXIDATION OF THE RUBBER PARTICLES AND TO INHIBIT COHESION THEREOF AND RECLAIMS THE RUBBER PARTICLES, AND DISCHARGING THE POWDER-COATED RECLAIMED RUBBER PARTICLES AS DISCRETE PARTICLES, THE POWDER BEING PRESENT IN A VOLUME OF AT LEAST 23% FO THE VOLUME OF THE SCRAP. 